Astronomers have discovered a rocky, low-mass planet orbiting the closest single star to Earth.
The exoplanet – known as Barnard b – was found around the famous Barnard's Star and is half the mass of Venus, with a year that lasts just over three Earth days.
The closest star system to Earth is Alpha Centauri, a three-star group, but Barnard's Star is the closest single star to our Solar System, a cosmic stone's throw at just six lightyears away.
What's more, observations hint at the existence of three more exoplanet candidates in orbit around the star.
And while the confirmed exoplanet is still much too far for any spacecraft to visit, the discovery marks a major step in the search for and study of nearby exoplanets.
How the Barnard's star exoplanet was found
A team of astronomers used the European Southern Observatory's Very Large Telescope (ESO's VLT) to find exoplanet Barnard b.
A potential detection had been made in 2018, but the exoplanet around Barnard's star had not been confirmed until now.
The team used ESPRESSO, an instrument designed to measure the wobble of a star caused by the gravitational pull of exoplanets in orbit.
Results were confirmed by data from other exoplanet instruments like HARPS at ESO's La Silla Observatory, HARPS-N and CARMENES.
The data does not support the existence of the exoplanet reported in 2018.
The discovery was announced in a paper published in the journal Astronomy & Astrophysics and follows 5 years of observations made with the VLT, located at the Paranal Observatory in Chile.
"Even if it took a long time, we were always confident that we could find something," says Jonay González Hernández at the Instituto de Astrofisica de Canarias in Spain, lead author of the paper.
The astronomers were searching for signals from possible exoplanets within the habitable zone of Barnard's star.
This is the orbital distance from a star at which liquid water could exist on a planet's surface.
Water being a key ingredient for life as we know it, its presence in liquid form is one condition that could make a planet habitable.
Red dwarfs like Barnard's star are targeted by exoplanet-hunters because low-mass rocky planets are easier to find than those orbiting larger, Sun-like stars.
What we know about exoplanet Barnard b
The newly-discovered rocky exoplanet around Barnard's star is known as Barnard b.
This is the exoplanet-naming convention that catalogues planets discovered around stars beyond our Solar System.
Barnard b is 20 times closer to Barnard's star than Mercury is to the Sun.
Its year lasts 3.15 Earth days – that's how long it takes to complete one orbit – and the exoplanet has a surface temperature around 125°C (257°F).
"Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth. But the planet is too close to the host star, closer than the habitable zone," explains González Hernández.
"Even if the star is about 2500 degrees cooler than our Sun, it is too hot there to maintain liquid water on the surface. "
"We now need to continue observing this star to confirm the other candidate signals," says Alejandro Suárez Mascareño, a researcher also at the Institute of Astrophysics of the Canary Islands and co-author of the study.
"But the discovery of this planet, along with other previous discoveries such as Proxima b and d, shows that our cosmic backyard is full of low-mass planets ."
Read the full paper on the discovery of exoplanet Barnard b at www.aanda.org/articles/aa/full_html/2024/10/aa51311-24/aa51311-24.html
